Non-Hermitian morphing of topological modes

Area of Science:

• Condensed Matter Physics
• Topological Materials
• Non-Hermitian Systems

Background:

• Topological modes (TMs) are typically confined to defects or boundaries.
• The non-Hermitian skin effect (NHSE) causes bulk states to localize at boundaries.

Purpose of the Study:

• To investigate how NHSE can reshape TMs.
• To delocalize TMs from boundaries and explore their behavior in bulk lattices.

Main Methods:

• Exploiting NHSE in topological lattices.
• Analyzing the critical non-Hermitian parameter for mode delocalization.
• Experimental realization in 1D, 2D, and higher-order active mechanical lattices.

Main Results:

• TM wavefunctions are reshaped by NHSE, becoming delocalized.
• At a critical parameter, TMs extend across the entire bulk lattice ('extended mode outside of a continuum').
• These extended modes are topologically protected and robust against disorder.
• Diverse TM shapes achieved by engineering non-Hermiticity distribution.

Conclusions:

• NHSE provides a mechanism to control and delocalize TMs.
• Extended, topologically protected modes are demonstrated.
• Findings advance understanding of TMs and NHSE, opening avenues for topological applications.